The present studies aim: 1) to examine the usefulness of T-cell derived and N-cell derived macromolecular insoluble cold globulin as markers for identification of cell types in human lymphoid malignancies; 2) to study the possibility that T-MICG and N-MICG may serve as prognostic indicators in acute leukemia; 3) to determine whether MICG is a differentiation marker. In vitro studies will make use of fluorescein conjugated antiserum to T-MICG and N-MICG and fluorescent microscopy to examine stained normal and malignant cells. Normal and neoplastic cells will also be radiolabelled in vitro to determine the distribution of MICG in normal and pathological lymphocytes.